New scrolling and animation functionality for 8x8 Matrix components

In my personal project, I found the need to scroll images across the 8x8 matrix. I thought I would contribute this work back to the shared library so that everyone can benefit and save from time.

The new functionality has been added to the Matrix8x8 class. The BicolorMatrix8x8 also inherits these changes since it now inherits from the Matrix8x8 class.

The three most important new functions are the following:
1. **horizontal_scroll:** Returns a list of images which appear to scroll from left to right across the input image when displayed on the LED matrix in order.
2. **vertical_scroll:** Returns a list of images which appear to scroll from top to bottom down the input image when displayed on the LED matrix in order.
3. **animate:** Displays each of the input images in order, pausing for a configurable amount of time after each image.

I've tested these changes in my own project where I have about 30 different animations. In that project, I am using a Raspberry Pi B+ and a Bicolor Matrix component. Although the modifications I made should run well on all platforms, I've only tested it with limited hardware.

I've also expanded the example script for the Bicolor Matrix to demonstrate some of the new functionality. 

I would really love to see these changes pulled into the main repository. And if you felt so kind, I would really appreciate being listed as a contributor on the readme page. I'm a college student and it would be a nice boost to my resume to have a documented contribution to a great open source project like this.